Under the deal, a group of farmers who voluntarily cut water use by 25% won’t face mandatory cutbacks

California officials agreed Friday to let a group of farmers voluntarily reduce their water consumption by 25% in return for not mandating cuts, a deal that could ease pressure on dwindling supplies amid a historic drought.

Under the deal with the State Water Resources Control Board, farmers with “riparian” senior water rights in the Sacramento-San Joaquin Delta who voluntarily reduce their water use by 25% from 2013 levels won’t...